Capacitor discharge ignition system

ABSTRACT

A capacitor discharge ignition system which includes a storage capacitor, a charging circuit for charging the capacitor, a switch effectively directly connected across the output of the charging circuit and adapted to be actuated in timed relation with respect to an engine, wherein the charging circuit comprises a converter which stalls on actuation of the switch means which is connected to provide a low impedance short across the output of the converter to reset the converter and switch means in timed relation as a function of the engine speed. The switch includes a trigger circuit and a feedback circuit is provided to feed back a portion of the energy stored in the storage capacitor to effectively completely discharge the trigger circuit of the switch when actuated. There may further be provided means for supplying a reverse gate voltage to the switch means to prevent spurious signals from actuating same.

United States Patent [72] Inventors Robert G. Van Houten;

John C. Schweitzer, both of Grand Junction, Colo. [21] Appl. No. 456,789[22] Filed May 18, 1965 [45] Patented Sept. 14, 1971 [73] Assignee DeltaProducts Inc.

Grand Junction, C010.

[54] CAPACITOR DISCHARGE IGNITION SYSTEM 9 Claims, 5 Drawing Figs.

[52] US. Cl. ..315/209 CD, 315/209 SC, 315/241 [51] Int. Cl. F02p 3/06,l-10lt 15/02 [50] Field oISear-eh 315/209 CD, 209, 241, 209 SC; 331/113.1

[56] References Cited UNITED STATES PATENTS 3,312,860 4/1967 Sturm315/223 3,329,867 7/1967 Steams 315/209 3,331,986 7/1967 Hardin et al..317/200 2,837,651 6/1958 Schultz 331/113 2,948,841 8/ 1960 Lucanthi etal.. 331111 B X 2,976,461 3/1961 Dilger et a1. 331/113 X 3,032,6845/1962 Kuykendall 315/209 X 3,056,066 9/ l 962 Dozier, .I r. 315/2233,078,391 211963 Bunodiere et a1... 315/209 X 3,219,877 11/1965 Konopa315/209 3,251,351 5/1966 Bowers 315/209 X OTHER REFERENCES June 1964issue of Popular Electronics" (Patent Office Scientific Library DateStamp of Receipt on May 11. 1964) pages 33- 44 inclusive and pages 85,86, and 87.

Primary ExaminerRoy Lake Assistant Examiner-E. R. LaRocheAttomey-Anderson, Spangler & Wymore ABSTRACT: A capacitor dischargeignition system which includes a storage capacitor, a charging circuitfor charging the capacitor, a switch effectively directly connectedacross the output of the charging circuit and adapted to be actuated intimed relation with respect to an engine, wherein the charging circuitcomprises a converter which stalls on actuation of the switch meanswhich is connected to provide a low impedance short across the output ofthe converter to reset the converter and switch means in timed relationas a function of the engine speed. The switch includes a trigger circuitand a feedback circuit is provided to feed back a portion of the energystored in the storage capacitor to effectively completely discharge thetrigger circuit of the switch when actuated. There may further beprovided means for supplying a reverse gate voltage to the switch meansto prevent spurious signals from actuating same.

PAIENIEDSEPMISTI 3504.978

sum 2 or 3 /-PLUG FIRES TYPICAL ms: TIME 0.5-2psec 3 I BRIDGE STOPSCONDUCTING 8 2 CAPACITOR I RECHARGES & l oou. RINGING 6| FREQUENCY n AAF 63/ V0.4 V 0.5 MILLISECONDS SRC TURN OFF 5 BRIDGE CONDUCTS E E 4 l II I I l I I I I 2 3 4 5 6 7 8 9 IO RPM in THOUSANDS I l I I l l l RPM inTHOUSANDS 4 INVENTOR.

ROBERT G. Vom HOUTEN JOHN C. SCHWEITZER PATENTED SEP] 4 l9)" SHEET 3 BF3 NNNJ OOOOOOO'OOOOO qOm ONN

INVENTOR. ROBERT G. Vom HOUTEN JOHN C. SCHWEITZER CAPACITOR DISCHARGEIGNITION SYSTEM The use of higher compression ratios in the modernautomobile and truck engines requires a higher voltage at the points ofthe spark plugs and greater dependability of the remaining circuitcomponents. Several attempts have been made to achieve the requiredresults by combining transistor amplifiers with gaseous discharge tubesand storage capacitors but these circuits have been expensive, bulky,and sometimes refuse to operate when one spark plug is short circuitedor refuses to fire because of too widely separated points. The circuitof the present invention utilizes relatively few elements, insures astrongly peaked sparking voltage pulse that causes a discharge at someof the spark plugs even though other plugs are disconnected or shorted.

The new ignition circuit for high compression engines is relativelyinexpensive as compared with those heretofore proposed. It increases thelife of spark plugs and reduces, if not eliminates, misfiring due tofouled plugs by providing a single high voltage pulse across the sparkplug terminals. The circuit effectively reduces the required currentthrough the breaker contacts, thus insuring longer contact life.

It is the principal object of the present invention to provide anignition circuit which will develop, in a simple controllable manner,high voltages and relatively high energies for delivery to a spark plugor spark gap to ignite combustible fuel mixtures.

A further important object of the present invention is the provision ofan improved ignition system having a variable spark repetition rateresponsive to engine speed.

It is a further object of the present invention to provide an ignitioncircuit which is efficient and will provide dependable operation over awide range of ambient temperatures, voltages, and energies inpredictable manner.

A further object of the present invention is the provision of animproved ignition system which provides for delivery of only onecomplete cycle to the ignition coil each time the points open.

A still further object of the present invention is to provide animproved ignition circuit which displays a rapid rise time and avoidsmost of the disadvantages of prior art ignition systems.

Another object of the present invention is to provide an improvedignition system which avoids refiring due to point bounce in high-speedengines.

Another important object of the present invention is to provide animproved ignition circuit which is capable of impressing a voltage andcurrent, with a minimum electrical loss, across the primary windings ofa high ratio step-up transformer or ignition coil, the output of whichis delivered to spark plugs or spark gaps.

In accordance with the present invention a relatively low DC voltage istransformed to an intermediate DC voltage by means of a DC to DCconverter and stored in a storage capacitor. Breaker contacts or othersuitable means are controlled to open and close in synchronism with themovements of the engine's pistons to provide a signal or conditionrepresentative of such movement. The signal or condition thus producedis used to control the discharge of the capacitor into a high ratiostepup transformer having the output thereof connected to deliver thedeveloped potential to spark plugs or spark gaps in timed sequence andin proper order to ignite a combustible fuel serving to drive an engine.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the following detaileddescription taken in connection with the accompanying drawings and itsscope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is a schematic diagram of connections of the preferred form ofthe ignition circuit of the invention;

FIG. 2 is a graph showing the voltages developed across the ignitioncoil primary windings during the operation of the circuit of thisinvention as a function of time;

FIG. 3 is a graph showing power supplied to the ignition circuit of thisinvention as a function of engine speed;

FIG. 4 is a graph showing the high tension voltage developed at thespark plugs by the ignition circuit of this invention as a function ofengine speed; and

FIG. 5 is a schematic diagram of connections similar to FIG. 1 butemploying a modified control arrangement.

Referring now to FIG. 1, the circuit includes the usual battery 10 andbreaker points 12 which are operated by a portion of the mechanicalgearing coupled to a drive shaft. Although the circuit is illustrated asusing breaker points as the means of synchronizing operation of thecircuit with the movement of the engine, it will be readily understoodby those skilled in the art that other control means and methods may beused with equal success that make use of magnetic, photoelectrical orHall effect characteristics to sense the appropriate moment for firingand develop a control signal suitable to control the ignition circuit ofthe present invention.

The ignition circuit includes a DC to DC converter 14 to convert therelatively low voltage from battery 10 to a higher voltage for storage,a storage element or capacitor 16, a switching circuit 18 to control thedischarge of the storage element 16, a sensing means such as breakerpoints 12 to sense the relative position of engine parts, and actuateswitch 18 and a high voltage output transformer or coil 20 to transformthe voltage stored in capacitor 16 to a high tension voltage which willfire a spark plug. The output circuit includes the usual plu rality ofspark plugs represented by a single gap 22 and a distributor 24 whichmay be operated by a mechanical gear means coupled to the drive shaft ofthe engine. The operation of the distributor and the spark plugs arewell known and need not be described here in detail.

The converter 14 includes transformer 26 having a center tapped 27primary winding 28 connected to the positive terminal of battery 10 viaconductor 30 and ignition switch 31. Each end of the primary winding isconnected to the base electrode 32 and 34 respectively of transistors 36and 38 serially through base-current-limiting resistors 40 and 42.Intermediate taps 44 and 46 to either side of the center of the primarywinding 28 are connected respectively to the emitter electrodes 48 and50 of transistors 36 and 38. The collector electrodes 52 and 54 areconnected serially through forward bias resistors 56 and 58 to baseelectrodes 32 and 34 respectively and are further connected to groundpotential via conductor 60. The secondary winding 62 of transformer 26is connected to a diode rectifier bridge 63 comprising diodes 64, 66, 68and 70. The negative terminal of rectified output of bridge 63 isconnected via conductor 72 to one lead of filter condenser 74 with theother lead being connected to ground potential. A diode 76 is connectedbetween the center tap 27 of the primary winding of transformer 26 andthe positive lead of condenser 74 which acts as a filter to reduce anyvoltage ripple present on the battery supply as it is passed throughdiode 76 to the switching circuit 18. Resistors 56 and 58 of theoscillator converter 14 serve as forward bias resistors enabling theoscillator to start at low temperatures and resistors 40 and 42 set thedrive level of the feedback signal to transistors 36 and 38.

The switching circuit 18 contains the silicon-controlled rectifiercontrol circuit and associated protective circuits. Thesilicon-controlled rectifier 78 has the cathode 80 thereof connected tothe negative terminal 82 of bridge 63 via conductors 84 and 72. Theanode 85 of rectifier 78 is connected to the positive terminal 86 of thebridge 63 via conductor 88. A high resistance bleeder resistor 90 isconnected between the anode 85 and the cathode 80 of the rectifier 78.The cathode 80 of rectifier 78 is connected to the common connection 21of the primary and secondary windings of coil 20 via conductor 92. Theanode 85 of rectifier 78 is connected to the other end of the primarywinding of coil 20 serially through storage capacitor 16 via conductor94. The gate electrode 96 of rectifier 78 is connected serially througha resistance 98 to the ungrounded contact 13 of the breaker points 12via conductor 100. A resistance 102 is connected between contact 13 ofthe points and conductor 92 to receive current from the junction ofdiode 76 and condenser 74 via conductor 84. The contact 13 of the pointsis also connected to the gate electrode of rectifier 78 serially throughcondenser 104, resistor 106, and conductor 108. A diode 110 is connectedin shunt with resistor 106 and diode 112 is connected between thejunction of condenser 104 and resistor 106 and ground potential existingon conductor 60. A resistor 114 is connected between ground potential onconductor 60 and the juncture 115 of gate electrode 96, resistor 106 anddiode 110. A further diode 116 is connected between juncture 115 andcathode electrode 80. The coil side of storage capacitor 16 is connectedto the juncture of condenser 104, diodes 110 and 112, and resistor 106serially through resistor 118 and diode 120.

The operation of the ignition circuit is as follows: On closure of theignition switch 31 battery voltage is supplied from battery to thecenter tap 27 of transformer 26 and to diode 76. The application ofvoltage to the transformer causes to flow through resistors 40, 42, 56and 58 and simultaneously through transistors 36 and 38 to ground. Sincethese paths have a different resistance value, one-half of the primarywinding will have a higher current flow.

Assuming that the upper half of the primary winding 28 carries slightlyhigher current than the lower, the voltages developed, in the twofeedback windings connecting resistors 40 and 42, tend to turntransistors 36 on and 38 off. This increases the current through theupper half of the transformer winding. The increase in current furtherdrives transistors 36 into conduction and transistors 38 into cutoff,simultaneously transferring energy to the secondary of transformer 26that is rectified by the diode bridge 63.

When the current through the upper half of the primary of transformer 26reaches a point where it can no longer increase, due to resistance inthe primary circuit and/or transformer core saturation, the signalapplied to the transistor 36 from the feedback winding decreases. Sincetransistor 36 immediately turns off, the current in the upper windingdecreases. The magnetic field developed by the current flow starts tocollapse. This collapsing field, cutting across all the windings in thetransformer, develops voltages in the transformer opposite in polarityto the voltage developed by the expanding field. This voltage now drivestransistor 36 into cutoff and transistor 38 into conduction andsimultaneously delivers power to the diode bridge 63. Once started, thisaction alternates, without load, at approximately 50 cycles per second.

The voltage applied to the diode bridge is rectified to a DC potentialof about 400 volts, charging capacitor 16 through the coil 20, connectedthrough the minus and plus coil terminals to the negative terminal ofthe diode bridge. This action takes place as soon as power is applied byturning on the ignition key. Simultaneously, voltage is applied from thebattery through diode 76 to capacitor 74 (serving as a filter to reduceany voltage ripple present on the battery supply). This filtered voltagethen flows through resister 102 to ground, if the distributor point 12is closed, or through condenser 104 and the silicon-controlled rectifiergate electrode 96 if the point is open.

Assume that the point is closed and the ignition switch 31 is closed asthe first cylinder comes up on compression and reaches the positionwhere the spark plug should be fired, the point 12 opens. The currentavailable at the junction of diode .76 and condenser 74 now flowsthrough resistor 102, condenser 104 and diode 110 to the gate of thesilicomcontrolled rectifier 78. This current switches the rectifier on.

When the rectifier turns on, two things happen simultaneously. Thesilicon-controlled rectifier short circuits the power supply (the energyis absorbed in the transformer 26) and the effect of the short reflectedto the primary of transformer 26 removes the drive from transistors 36and 38 stopping converter operation. The rectifier 78 also connects thepositive side of capacitor 16 to the plus coil terminal. This forms aclosed circuit consisting of the capacitor 16, silicon-controlledrectifier 78, and coil 20 primary winding. The energy stored in thecapacitor 16 is now delivered to the ignition coil 20. The coil primaryvoltage rises from 0 to 400 volts in approximately 2 microseconds, FIG.2.

The rise time of a standard ignition coil secondary is slower than therise time of its primary because of reflected secondary capacitance andprimary leakage inductances. A typical secondary rise time isapproximately 15 microseconds.

ln the circuit made up of the silicon-controlled rectifier 78, capacitor16, and coil 20, a resonant circuit is formed between the primary coilinductance and capacitor 16. The flywheel effect of this circuitrestores unused energy to the capacitor 16, the capacitor dischargecurrent flows through the rectifier 78 and coil primary creating amagnetic field in the coil 20. Current produced by the coils magneticfield continues to flow in the circuit until the capacitor 16 is chargedin a reverse direction to approximately 300 volts.

At this point the current attempts to reverse through the rectifier 78causing the same to return to its off condition. The direction ofcurrent and voltages causes the diode bridge 63 to conduct as a shortcircuit (all diodes simultaneously in a conduction mode). This currentflow discharges the capacitor 16 to zero from its reverse direction andrecharges the capacitor 16 toward its normal state. The remaining energyis stored in the circuit. When the current supplied by the coilinductance drops to zero, the bridge returns to a normal state, the loadis removed from transformer 26 and normal converter operation resumes.

As designed, the power supply of the present ignition system meets twoimportant requirements: it is stable when short circuited by therectifier, and it is resistant to parasitic oscillations under thoseconditions. High frequency or parasitic oscillations could destroy theinverter transistors by feeding power to the diode bridge 63. Therectifier 78 would continue to conduct, causing losses in thetransformer and associated circuitry. The inverter transistors 36 and 38are rated at 7 amperes each. They normally carry a maximum of 2 amperes.Parasitic oscillations would cause the power supply to draw currents of15 to 20 amperes causing their destruction or require more expensiveunits.

The normal operating frequency of the power supply, without spark load,is in the 50 to 60 c.p.s. range. Since the spark repetition rate of aneight-cylinder engine a 6,000 r.p.m. is 400 pulses per second, afrequency of 50 cycles will not supply the energy needed. As a result,the power supply changes its repetition rate, as the transformer isreset to a zero flux condition, by the signal coupled back through thediode bridge during the spark cycle. This restarting of the oscillatorto follow its load frequency causes the input power to the unit toincrease in direct ratio to engine speed. See FIG. 3.

The power supply will deliver full energy to the capacitor at enginespeeds over 8,000 r.p.m. Between spark pulses the converter has plentyof time to recharge the capacitor. Since its current drain is low, theignition circuit operates normally using the ballast-dropping resistoralready in most vehicles. This eliminates, in contrast to transistorsystems, rewiring the vehicle and/or adding an ignition relay.

As the engine continues to turn off compression, the converter rechargesthe capacitor for the next compression cycle. This enables the SCRignition system to deliver much higher energies during the startingcycle than would be possible if the energy were to be stored during thecompression cycle when battery voltage is lowest.

This removes the major handicap of SCR capacitive discharge systemstheinability of the silicon-controlled rectifier to turn off. Since the SCR78 will always turn off when voltages are removed, and the converter 14cannot restart due to the reflected load until the SCR is off, it isimpossible for this system to refuse to reset between spark pul ses.Thus a primary problem in previous designs of SCR ignitions has beensolved.

Since silicon-controlled rectifiers radically change sitivity withtemperature, something must be done to supply trigger, or gate, currentto fire the SCR over a low temperature range of 50 to 65F. Resistor 102and capacitor 104 deliberately overdrive the SCR 78 (in current) at thelowest operating temperature and voltage. High temperatures could causemultiple firing of the SCR-this is detrimental to a spark plug life andengine operation. Resistor 118 and diode 120 couple a negative pulsefrom the ignition coil 20, completely reverse charging condenser 104, assoon as the silicon-controlled rectifier 78 switches on. Diode 112serves to clamp the potential on condenser 104 at ground potential. Thisremoves the gate pulse and assures that only one complete cycle will bedelivered to the coil each time the points open. Diode 116 and resistors114 and 118 apply a normal reverse-gate voltage to the SCR 78 so thatany ripple voltage still in the gate circuit will not cause the SCR tofire except from a definite breaker point signal.

Silicon-controlled rectifiers have another important characteristic inelectronic ignition systems. The gate-firing characteristic of the scris primarily a function of time, as long as the supplied current isabove the minimum required to fire same. The modulation characteristicof the transistor is not present. Dirty or contaminated points do notdegrade the spark energy. The system of this invention will operateexcellently with points that could not be used in either a Kettering ora transistor ignition.

Since silicon-controlled rectifiers may be triggered by a current pulseof very short duration, it is necessary to prevent point bounce onclosure. Point bounce problems are one of the inherent limitations to ahigh-speed point operation. To remove the possibility of refiring bypoint bounce, diode 110 and resistor 106 introduce a predetermined delayof approximately 1 millisecond in recharging capacitor 104 when thepoints 12 close. The spark plugs are properly fired in speed ranges muchin excess of those of either a standard ignition system or transistorsystem. Analysis of high-speed operation of the SCR ignition circuit ofthis invention shows that accurate ignition control of timing may beobtained in excess of 10,000 r.p.m. with only minor care being used inpoint of adjustment as shown in the graph of FIG. 4.

Resistor 90 is present to discharge capacitor 16 when the ignitionswitch is opened. This prevents any shock hazard during servicing of theignition system. Resistors 40 and 42 are basecurrent-limiting resistorscontrolling the drive currents supplied, and resistors 56 and 58forward-bias transistors 36 and 38 to assure starting at lowtemperatures.

Transistor ignition systems, in general, require the removal of thecapacitor installed in the distributor. The SCR system of this inventionoperates either with or without this distributor capacitor. The onlyeffect of the distributor capacitor is to reduce the SCR firing current,since resistor 102 must supply charge current to it as well as condenser104. Resister 102, however, is sufficiently low in value to supply overtwo times the maximum required current to the SCR even with thedistributor capacitor installed.

Ignition systems with rapid rise time provide better performance infiring fouled plugs-as less total energy is wasted in the foulingresistance. 1f the secondary of the ignition coil is considered toconsist of an airgap shunted by resistance, then the energy dissipatedin the shunting resistance is directly dependent upon the time requiredto reach the ionization potential of the airgap. Silicon controlledrectifier systems are capable of very rapid rise times and have theability to fire spark plugs with low shunting resistance.

The rise time of the SCR system is dependent, to a large extent, on coilcharacteristics. However, its rise time to fire is more rapid than aKettering system with the same coil. The SCR ignition unit has beendesigned to fit existing vehicles without modification but even morerapid rise times-in the 2 microsecond range-could be supplied with aspecial coil.

The energies delivered by this SCR system to the spark plug are easilycontrolled by the capacitance value of capacitor 16, but may be raisedby increasing the value of this capacitor. As

gate senenergy to the coil primary.

designed, it is capable of delivering milliwatt-seconds of Assuming acoil efficiency of 50 percent, total spark energy delivered would be 40milliwattseconds or a substantial increase over the energy of standardsystems.

lf much higher energies should be needed in the future, system redesignwould consist of either increasing the value of capacitor 16 orincreasing the voltage supplied by the power supply. The new energylevel increases directly with the capacitance or with the square of thevoltage.

Thus it will be seen that the energy transfer ignition system of thisinvention provides energy levels substantially in excess of any presentignition system and ease of control thereof. Further the circuitprovides a much more rapid rise time than the known Kettering systemusing the same coil. Further point life is limited inly by mechanicalwear and point condition is relatively unimportant, as is dwell time,providing a system having higher reliability than others now being used.The current load on the battery using this circuit is substantially lessthan in the Kettering system and only about 20 percent that of mosttransistor systems.

Referring now to the embodiment of FIG. 5 the circuit includes the usualbattery 210 and breaker points 212 which are operated by a portion ofthe mechanical gearing coupled to a drive shaft. Although the circuit isillustrated as using breaker points as the means of synchronizingoperation of the circuit with the movement of the engine, it will bereadily understood by those skilled in the art that other control meansand methods may be used with equal success that make use of magnetic,photoelectrical or Hall effect characteristics to sense the appropriatemoment for firing and develop a control signal suitable to control theignition circuit of the present invention.

The ignition circuit includes a DC to DC converter 214 to convert therelatively low voltage from battery 210 to a higher voltage for storage,a storage element or capacitor 216, a switching circuit 218 to controlthe discharge of the storage element 216, a sensing means such asbreaker points 212 to sense the relative position of engine parts andactuate switch 218 and a high voltage output transformer 0r coil 220 totransform the voltage stored in capacitor 216 to a high tension voltagewhich will fire a spark plug. The output circuit includes the usualplurality of spark plugs represented by a single gap 222 and adistributor 224 which may be operated by a mechanical gear means coupledto the drive shaft of the engine. The operation of the distributor andthe spark plugs are well known and need not be described here in detail.

The converter 214 includes transformer 226 having a center tapped 227primary winding 228 connected to the positive terminal of battery 210via conductor 230 and ignition switch 231. Each end of the primarywinding is connected to the base electrode 232 and 234 respectively oftransistors 236 and 238 serially through base-current-limiting resistors240 and 242. Intermediate taps 244 and 246'to either side of the centerof the primary winding 228 are connected respectively to the emitterelectrodes 248 and 250 of transistors 236 and 238. The collectorelectrodes 252 and 254 are connected serially through forward biasresistors 256 and 258 to base electrodes 232 and 234 respectively andare further connected to ground potential via conductor 260. Thesecondary winding 262 of transformer 226 is connected to a dioderectifier bridge 263 comprising diodes 264, 266, 268 and 270. Resistors256 and 258 of the oscillator converter 214 serve as forward biasresistors enabling the oscillator to start at low temperatures andresistors 240 and 242 set the drive level of the feedback signal totransistors 236 and 238. The negative terminal 282 of the rectifiedoutput of bridge 263 is connected via conductor 272 to one end 221 ofthe primary winding of ignition coil 220, the other end of which isconnected serially through storage condenser 216, shunted by resistor290, to the positive terminal 286 of the bridge rectifier 263. Thediodes 264, 266, 268 and 270 of rectifier 263 rectify the output oftransformer 226, and in the process due to the filtering action ofcondenser 216 reduces the spiking" which would otherwise require muchhigher voltage rated transistors for 236 and238.

The control circuit 218 comprises a silicon-controlled rectifier or SCR278 having the anode 285 thereof connected to the positive terminal 286of bridge 263 and the cathode 280 also connected to end 221 of ignitioncoil 220. The gate electrode 296 thereof is connected serially throughcondenser 304 to ground. Diode 310 shunted by resistor 306 connects gate296 and cathode 280. Diode prevents excess reverse voltage from beingapplied between gate 296 and cathode 280 between firing intervals andduring the charging of condenser 304. Resistor 306 serves to reduce thepossibility of circuit leakages which might trigger SCR 278. Condenser304 is an energy storage capacitor which is discharged through SCR 278to turn on same and energize coil 220 for firing.

The control circuit further includes transistor 130 having theco|lector"l32 thereof connected to cathode 280 of SCR 278 and theemitter 134 thereof is connected through resistor 136 to groundpotential and also connected through resistor 138 to battery 210 throughswitch 231 via conductor 230. The base 140 of transistor 130 is alsoconnected to the battery 210 in similar manner through resistor 142.Resistor 142 is a base bias resistor used to turn transistor 130 on whenthe points 212 open while resistors 136 and 138 act as a voltage dividerto provide a bias during the time the transistor is not conducting inorder to prevent false triggering die to primary ripple or noise. Thecathode of transistor 130 is connected to battery 210 through resistor144.

The circuit of FIG. operates as follows: On closure of switch 231, powerfrom battery 210 is applied to the center tap 227 of transformer 226.Since the resistances across transistors 236 and 238 will not be equal,one or the other will draw more current through the transformer primaryto ground. The initial current surge produces an induced current to thefeedback winding (the end turns of the transformer primary) driving thistransistor towards conduction and simultaneously driving the oppositetransistor towards cutoff. As

the current rises and reaches the point of transformer core saturation(or where the current can no longer rise due to primary resistance,i.e., ballast resistor) the collapsing magnetic field drives thisconducting transistor towards cutoff and switches the oppositetransistor on. This occurs with no load or at engine idle atapproximately 50 cycles per second. Due to the developed cutoff biasproduced by the transformer feedback windings the transistors willoperate at much higher temperatures than is possible in a transistorignition system. The alternating current field induced by this actiongenerates a stepped up voltage in the secondary windings, multiplied bythe ratio of the transformer (approximately 25 times the batteryvoltage), or at nominal battery voltage of 14 volts, approximately 400volts. This 400-volt output square wave is rectified in the diode bridge263 and charges capacitor 216 to the peak voltage of 400 volts.Simultaneously with this action, the battery potential applied to thetransformer primary also flows through resistor 144 and diode 310 andcharges capacitor 304 to the battery potential, points being closed. Thesystem is now ready to fire the coil.

The points, opening, remove the ground from the distributor tenninal,causing the battery voltage, which has been flowing through 142 toground, to raise the base voltage of transistor 130 to nominal batteryvoltage, causing it to conduct. The energy stored in capacitor 304 andthe current through resistor 144 now discharge through transistor 130 toground. Since the silicon-controlled rectifier 278 becomes an extremelylow resistance when fired, capacitor 216 discharges through SCR 278 andthe coil 220, thus developing an applied voltage peak of 400 voltsacross the coil with a peak surge current of approximately 400' timesthe coil ratio or with a 200 to 1 ratio coil, 80,000 volts. Since asilicon-controlled rectifier is an extremely rapid switch, the time forthe secondary voltage to rise is approximately equal to the turn on timeof the silicon-controlled rectifier, or oneor two-millionths of asecond.

Due to the inherent inductance of the ignition coil an oscillatoryresponse or flywheel action takes place causing the current to reversewhen the capacitor 216 reaches a state of zero charge. Since it is aninherent characteristic of a silicon-controlled rectifier to turn offand become nonconductive when the current becomes zero or is reversed,SCR 278 now turns off and capacitor 216 is recharged by the powersupple.

At high engine r.p.m.'s the spark pulse rate approaches 600 cycles persecond, and the power supply requires at least onehalf cycle to rechargecapacitor 216. it is therefore essential that the converter frequencyfollow the engine speed. For example, it would be impossible to developthe required amount of energy if the converter were to continue tooperate 50 cycles when the spark pulse rate might be 300 or 400 cyclesper second. This circuit is unique in that it is so designed that theconverter does follow the pulse or spark repetition rate. This isaccomplished as follows: During the time that the silicon-controlledrectifier SCR 278 is turned on and discharging capacitor 216, it alsoplaces an effective short circuit across the output of the power supply.This absorbs the energy which might be stored in the transformer coreand effectively cause the converter to restart, regardless of the statethat it may be in during a cycle. lt also might be interpreted that thisshort circuit reduces the transformer inductance thus allowing it tooperate at a much higher frequency. Since the point of interruption,during the oscillator converter cycle, is random, the load tends todivide on alternate half cycles, thus equalizing the energy supplied bytransistors 236 and 238. It is also essential that the transformer corebe reset on alternate cycles in order to develop sufficient energy. Thismethod of operation insures core resetting.

Thunderbolt is unique in its circuitry since it is the first unit of itstype to use a silicon-controlled rectifier in an energy storage system.The variable frequency operation of the oscillator is unique, as is thetransistor switching of the silicon-con trolled rectifier. Thesecircuits are the basic heart of the circuits operation, and account forits extreme efficiency and reliability. This method of operation alsoaccounts for the extreme ease of installation, since the efficienciesare many times higher than any ignition system to date. This high effciency allows the circuit to operate over extremes of input resistance,and voltages not acceptable by any other ignition system. The circuit ofthis invention can serve as the primary building block for completeignition control systems including electrical spark advance and retard.

While there have been described what at present are considered to be thepreferred embodiments of this invention, it will be obvious tothoseskilled in the art that various changes and modifications may bemade therein without departing from the invention. It is aimed thereforein the appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

What is claimed is:

1. An ignition circuit for internal combustion engines and rotatingturbine engines having a spark plug in each combustion chambercomprising a source of direct current, a charging circuit includingconverter means having an input connected to said current source and anoutput adapted to develop a relatively high DC potential, said converterbeing substantially devoid of parasitic oscillation on being shortcircuited, a storage capacitor connected to the converter output to becharged thereby, a discharge circuit including the capacitor, aswitching means, and an input winding of an output transformer, saidtransformer having a winding connected to said spark plugs, sensingmeans adapted to develop signals in response to the predeterminedpositioning of an engine part representative of the occurrence of apreselected portion of the engine cycle and control means adapted toactuate said switching means in response to a signal developed by saidsensing means and discharge said discharge capacitor through saidswitching means and said output transformer winding to fire said sparkplugs, wherein said control means includes electrical storage meansadapted to transfer electrical energy to said switching means to actuatesame in response to a signal from said sensing means and a feedbackmeans connected between said output transformer and said electricalstorage means adapted to feed a small portion of the electrical energydeveloped in said output transformer to said electrical storage means tosubstantially completely reverse charge same on discharge of thedischarge capacitor thereby to prevent more than a single effectivedischarge in the discharge circuit during a single discharge cycle.

2. The circuit of claim 1 including delay means with unidirectionalcurrent means adapted to introduce a predetermined time delay before theelectrical storage means of the control means can be recharged after asignal from the sensing means has been received and the electricalenergy has been transferred.

3. An ignition circuit according to claim 1 wherein the charging circuitincludes a converter having a variable repetition rate and beingresponsive to the application of a low impedance load thereto tointerrupt operation and responsive upon removal of such load to resumeoperation.

4. The circuit of claim 1 wherein said switching means includesrectifier means having a cathode and a switching electrode formingtriggers of opposite polarity, signal path means connecting both saidcathode and said switching electrode to potentials of opposite polarityto apply a reverse gate voltage thereto in the absence of a developedsignal from the sense means.

5. The circuit of claim 4 wherein the signal path means connected tosaid cathode further includes a unidirectional current means and acharge storage means, which storage means serves to reverse bias therectifier means whenever the DC potential of the charging circuit fallsbelow the potential of the charge storage means.

6. An ignition circuit for internal combustion engines and rotatingturbine engines having a spark plug in each combustion chambercomprising: a source of direct current; a DC to DC converter connectedthereto including a pair of transistors, transformer means coupling saidtransistors through the primary winding thereof to provide a variablefrequency oscillator circuit including a portion of the transformerprimary winding in the feedback circuit thereof, and rectifier meansconnected across the secondary winding of said transformer to rectifythe output signals developed in the secondary winding of the convertertransformer; an output transformer having a primary winding and anoutput winding; a storage capacitor serially connected across the outputof said converter; switching means also connected across the output ofthe converter in parallel with said output transformer and saidcapacitor; control means adapted to actuate said switch means to providea short circuit low impedance electrical path therethrough for thedischarge of an electrical charge stored in the storage capacitorthrough the output transformer and at the same time by means of areflected load from the secondary winding of the converter transformerto the primary winding thereof to effectively remove the drive to thetransistor oscillators and momentarily interrupt the operation of theconverter, which operation will resume upon the opening of saidswitching means; and, sensing means responsive to the movement ofcomponent parts of an engine to develop signals as a function of timerepresentative of the proper timing to be applied to said control meansto actuate said switch means and apply firing potential to the sparkplugs from said output winding in timed relation to the movement of theengine, wherein said control means includes electrical storage meansadapted to transfer electrical energy to said switching means to actuatesame in response to a signal from said sensing means and a feedbackmeans connected between said output transformer and said electricalstorage means adapted to feed a small portion of the electrical energydeveloped in said output transformer to said electrical storage means tosubstantially completely reverse charge same on discharge of thedischarge capacitor thereby to prevent more than a single effectivedischarge in the discharge circuit during a sin le discharge cycle.

7. lhe circuit of claim 6 including delay means adapted to introduce apredetermined time delay before the electrical storage means of thecontrol means can be recharged after a signal from the sensing means hasbeen received and the electrical energy has been transferred.

8. The circuit of claim 6 wherein said switching means includesrectifier means having a cathode and a switching electrode formingtriggers of opposite polarity, signal path means connecting both saidcathode and said switching electrode to potentials of opposite polarityto apply a reverse gate voltage thereto in the absence of a developedsignal from the sensing means.

9. The circuit of claim 8 wherein the signal path means connected tosaid cathode further includes a unidirectional current means and acharge storage means, which storage means serves to reverse bias therectifier means wherever the DC potential of the charging circuit fallsbelow the potential of the charge storage means.

1. An ignition circuit for internal combustion engines and rotatingturbine engines having a spark plug in each combustion chambercomprising a source of direct current, a charging circuit includingconverter means having an input connected to said current source and anoutput adapted to develop a relatively high DC potential, said converterbeing substantially devoid of parasitic oscillation on being shortcircuited, a storage capacitor connected to the converter output to becharged thereby, a discharge circuit including the capaciTor, aswitching means, and an input winding of an output transformer, saidtransformer having a winding connected to said spark plugs, sensingmeans adapted to develop signals in response to the predeterminedpositioning of an engine part representative of the occurrence of apreselected portion of the engine cycle and control means adapted toactuate said switching means in response to a signal developed by saidsensing means and discharge said discharge capacitor through saidswitching means and said output transformer winding to fire said sparkplugs, wherein said control means includes electrical storage meansadapted to transfer electrical energy to said switching means to actuatesame in response to a signal from said sensing means and a feedbackmeans connected between said output transformer and said electricalstorage means adapted to feed a small portion of the electrical energydeveloped in said output transformer to said electrical storage means tosubstantially completely reverse charge same on discharge of thedischarge capacitor thereby to prevent more than a single effectivedischarge in the discharge circuit during a single discharge cycle. 2.The circuit of claim 1 including delay means with unidirectional currentmeans adapted to introduce a predetermined time delay before theelectrical storage means of the control means can be recharged after asignal from the sensing means has been received and the electricalenergy has been transferred.
 3. An ignition circuit according to claim 1wherein the charging circuit includes a converter having a variablerepetition rate and being responsive to the application of a lowimpedance load thereto to interrupt operation and responsive uponremoval of such load to resume operation.
 4. The circuit of claim 1wherein said switching means includes rectifier means having a cathodeand a switching electrode forming triggers of opposite polarity, signalpath means connecting both said cathode and said switching electrode topotentials of opposite polarity to apply a reverse gate voltage theretoin the absence of a developed signal from the sense means.
 5. Thecircuit of claim 4 wherein the signal path means connected to saidcathode further includes a unidirectional current means and a chargestorage means, which storage means serves to reverse bias the rectifiermeans whenever the DC potential of the charging circuit falls below thepotential of the charge storage means.
 6. An ignition circuit forinternal combustion engines and rotating turbine engines having a sparkplug in each combustion chamber comprising: a source of direct current;a DC to DC converter connected thereto including a pair of transistors,transformer means coupling said transistors through the primary windingthereof to provide a variable frequency oscillator circuit including aportion of the transformer primary winding in the feedback circuitthereof, and rectifier means connected across the secondary winding ofsaid transformer to rectify the output signals developed in thesecondary winding of the converter transformer; an output transformerhaving a primary winding and an output winding; a storage capacitorserially connected across the output of said converter; switching meansalso connected across the output of the converter in parallel with saidoutput transformer and said capacitor; control means adapted to actuatesaid switch means to provide a short circuit low impedance electricalpath therethrough for the discharge of an electrical charge stored inthe storage capacitor through the output transformer and at the sametime by means of a reflected load from the secondary winding of theconverter transformer to the primary winding thereof to effectivelyremove the drive to the transistor oscillators and momentarily interruptthe operation of the converter, which operation will resume upon theopening of said switching means; and, sensing means responsive to themovement of component parts of an engine to develop signals As afunction of time representative of the proper timing to be applied tosaid control means to actuate said switch means and apply firingpotential to the spark plugs from said output winding in timed relationto the movement of the engine, wherein said control means includeselectrical storage means adapted to transfer electrical energy to saidswitching means to actuate same in response to a signal from saidsensing means and a feedback means connected between said outputtransformer and said electrical storage means adapted to feed a smallportion of the electrical energy developed in said output transformer tosaid electrical storage means to substantially completely reverse chargesame on discharge of the discharge capacitor thereby to prevent morethan a single effective discharge in the discharge circuit during asingle discharge cycle.
 7. The circuit of claim 6 including delay meansadapted to introduce a predetermined time delay before the electricalstorage means of the control means can be recharged after a signal fromthe sensing means has been received and the electrical energy has beentransferred.
 8. The circuit of claim 6 wherein said switching meansincludes rectifier means having a cathode and a switching electrodeforming triggers of opposite polarity, signal path means connecting bothsaid cathode and said switching electrode to potentials of oppositepolarity to apply a reverse gate voltage thereto in the absence of adeveloped signal from the sensing means.
 9. The circuit of claim 8wherein the signal path means connected to said cathode further includesa unidirectional current means and a charge storage means, which storagemeans serves to reverse bias the rectifier means wherever the DCpotential of the charging circuit falls below the potential of thecharge storage means.